Metal containers used for beverage or food can be broadly categorized into a two-piece can and a three-piece can. For the two-piece can, which is typified by a DI can, drawing and ironing are performed, then, lacquering is applied on the inner surface side of the can, and lacquering and printing are applied on the outer surface side of the can. For the three-piece can, lacquering is applied on a surface corresponding to the inner surface of the can, printing is performed on a surface corresponding to the outer surface of the can, and then, welding is applied to a body portion of the can.
For both types of cans, the lacquering process is a necessary process performed before or after the can-making. With regard to lacquering, a solvent-based lacquer or water-based lacquer is used, and then, baking is performed. Through this lacquering process, waste materials such as waste solvents resulting from these lacquers are produced as industrial wastes, and exhaust gas (mainly carbon dioxide) is emitted to the atmosphere. In recent years, efforts for reducing these industrial wastes and exhaust gas have been undertaken with the aim of achieving global environmental protection. Among them, attention has been paid to a technique of laminating films as an alternative to the lacquers, and this technique is spreading rapidly.
For the two-piece can, there have been provided a large number of inventions concerning a method of manufacturing a can by laminating films, or other related methods. These inventions include, for example:    Patent Document 1 “Method of Manufacturing a Drawn and Ironed Can”;    Patent Document 2 “Drawn and Ironed Can”;    Patent Document 3 “Method of Manufacturing a Deep-drawn Thinned Can”; and    Patent Document 4 “Coated Steel Sheet for a Drawn and Ironed Can”.
For the three-piece can, there have been proposed:    Patent Document 5 “Film-layered Steel Strip for Three-piece Can, and a Method of Manufacturing the Same”;    Patent Document 6 “Three-piece Can Having Multiple-layered Organic Film on the Outer Surface of the Can”;    Patent Document 7 “Steel Sheet for a Three-piece Can Having Striped Multiple-layered Organic Film”; and    Patent Document 8 “Method of Manufacturing a Striped Laminate Steel Sheet for a Three-piece Can”.
In many cases, a chromate film subjected to an electrolysis chromate treatment is used for a steel sheet used as a base for the laminate film. The chromate film has a two-layered structure including a hydrated Cr oxide layer provided on the upper layer of a metal Cr layer. This provides the laminate film (adhesive layer in the case where the film has adhesive agent) with adhesiveness to the steel sheet by way of the hydrated Cr oxide layer of the chromate film. It is said that this appearance of adhesiveness results from a hydrogen bond between a hydroxy group of the hydrated Cr oxide and a function group such as a carbonyl group and an ester group of the laminate film, although details of a mechanism thereof are not clearly found.
Further, a technique employing a Zr compound film in place of the conventional chromate film includes:    Patent Document 9 “Steel Sheet for a Container Exhibiting Excellent Can-making Workability”;    Patent Document 10 “Steel Sheet for a Container”;    Patent Document 11 “Steel Sheet for a Container”; and    Patent Document 12 “Steel Sheet for a Container Exhibiting Excellent Organic Film Property, and a Method of Manufacturing the Same”.